Boating USA — January 2018

BOAT DOCTOR///BOAT DOC SPECIAL

32 | BOATINGMAG.COM | JANUARY 2018

include 5052 and

5086, which off er high

strength and corrosion

resistance; 6061 and

6063 alloys are often

used in extrusions; and

6463 fi nds applications

in tops, towers, rails and

leaning posts. (See “Ma-

rine Metals” for more

on aluminum alloys.)

GRADES OF

STAINLESS STEEL

Commodity-grade stain-

less steel is 304, but look

for 316-grade stainless

for marine accessories.

It contains molybde-

num and more nickel

for greater strength and

corrosion resistance,

and thus is preferred for

most marine applica-

tions. (See “Marine

Metals” for more on

stainless alloys.)

FINISHES

Make sure the stain-

less in the accessory

features a polished

fi nish, which allows the

chromium in the alloy

to react with oxygen

in the air to form an

invisible chrome-

oxide surface layer to

maximize corrosion

resistance. If surface

corrosion happens to

appear in the future,

it is relatively easy to

polish out.

Aluminum, on the

other hand, needs more

than polishing to resist

corrosion. Make sure

it is either anodized or

powder-coated. With

applied in ovens where

a spray coating of pow-

der is heated to melt

and chemically bond

to the metal surface.

Powder-coating is

easier to touch up and

repair than anodized

aluminum, says Chao.

expensive, and as — Jim Hendricks

indicated earlier, it’s

three times heavier

than aluminum. When

used for structures

such as hardtop

frames, it not only adds

weight aloft, but it

can also create stress,

resulting in fi berglass

fractures over time. To

prevent this, reinforce

the fi berglass at sup-

port points, says Chao.

GRADES OF

ALUMINUM

The best grades of

aluminum for marine

applications include

5000 and 6000 series

alloys, Chao says. Alloys

typically used for sheet

and plate aluminum

anodizing, parts are

dipped in a chemical

bath that essentially

oxidizes the surface,

but with an estheti-

cally pleasing texture

and sheen.

Powder-coating is

growing in popularity,

says Chao. This is

PHOTOS: (CLOCKWISE FROM TOP LEFT) COURTESY REGULATOR, COURTESY WEST MARINE (2), COURTESY BOSTON WHALER

+

MARINE METALS

ALUMINUM ALLOYS

(CONTENT PERCENTAGES)

5052 aluminum 95.7 to 97.7, chromium 0.15 to 0.35,

copper 0.1, magnesium 2.2 to 2.8, manganese 0.1,

silicon 0.25, zinc 0.1

5086 aluminum 93 to 96.3, chromium 0.05 to 0.25,

copper 0.1, magnesium 3.5 to 4.5, manganese 0.2

to 0.7, silicon 0.4, zinc 0.25

6061 aluminum 96 to 97.4, chromium 0.04 to 0.35,

copper 0.15 to 0.4, iron 0.7, magnesium 0.8 to 1.2,

manganese 0.15, silicon 0.4 to 0.8, titanium 0.15,

zinc 0.25

6063 aluminum 87.1 to 91.4, chromium 0.18 to 0.28,

copper 1.2 to 2, magnesium 2.1 to 2.9, manganese

0.3, silicon 0.4, zinc 5.1 to 6.1

6463 aluminum 97.9 to 99.4, copper 0.2, iron 0.15,

magnesium 0.45 to 0.9, manganese 0.05, silicon

0.2 to 0.6, zinc 0.05, residuals 0.15

STAINLESS-STEEL ALLOYS

(CONTENT PERCENTAGES)

304 iron 65 to 71, carbon 0.08*, chromium 18 to 20,

manganese 2, nickel 8 to 12, nitrogen 0.1, phos-

phorus 0.045, silicon 0.75, sulphur 0.03

316 iron 62 to 69, carbon 0.08*, chromium 16 to 18,

manganese 2, molybdenum 2 to 3, nickel 10 to

14, nitrogen 0.1, phosphorus 0.045, silicon 0.75,

sulphur 0.03

*304L and 316L contain 0.03 percent carbon

LIGHTEN UP

Towers and seat pedes-

tals are often aluminum to

minimize weight. Below:

Stainless-steel railings

resist bending.